1. Field of the Invention
The present invention relates generally to wireless devices that filter between multiple supported bands of operation, and more particularly relates to a cellular telephone that discriminately adjusts filtering levels to reduce insertion loss.
2. Background of the Invention
Manufacturers of wireless communication devices continuously strive to offer increasing functionality and features in their products. These advances are intended to lead to great convenience to the users and increased market share to the manufacture. As is often the case, combining features and functions on a single device requires coordination between the features and functions and frequent compromises between attributes, such as, speed, power, bandwidth, size, performance, and others.
The most basic function of a wireless communication device is, obviously, communicating with others. For standard wireless communication, a transmitter modulates data onto a radio frequency (RF) carrier signal and transmits the signal to a receiver. Conversely, a receiver in the wireless device receives RF signals and demodulates to determine and capture the data riding on the signal. Various transmission schemes are available and widely used. Some of these schemes include Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), or other wireless communication systems. A CDMA system may implement one or more CDMA standards such as IS-95, IS-2000 (also commonly known as “1x”), IS-856 (also commonly known as “1xEV-DO”), Wideband-CDMA (W-CDMA), and others. A TDMA system may implement one or more TDMA standards such as Global System for Mobile Communications (GSM). The W-CDMA standard is defined by a consortium known as 3GPP, and the IS-2000 and IS-856 standards are defined by a consortium known as 3GPP2. These standards are known to those of skill in the art.
One feature, in addition to cellular communication, that is now available on a select number of wireless devices is communication with satellites that belong to the well-known Global Position System (GPS). GPS communication can be used for a variety of purposes, but mainly for determining terrestrial position of the receiver. For instance, by calculating the length of time a signal takes to travel from the satellite to the wireless device, the device's distance from the satellite can be calculated. By using multiple satellites, a device's three-dimensional position on the earth can be determined with considerable accuracy. To utilize the GPS, the wireless device uses a separate GPS antenna designed to communicate in the GPS frequency range.
Table 1 shows the various frequency bands in which a wireless communication device may operate, although the devices are not limited to these example frequencies and the bands are not limited to the frequency ranges shown.
TABLE 1Frequency RangeFrequency BandPersonal Communication System (PCS)1850 to 1990 MHzCellular824 to 894 MHzDigital Cellular System (DCS)1710 to 1880 MHzGSM900890 to 960 MHzInternational Mobile1920 to 2170 MHzTelecommunications- 2000 (IMT-2000)CDMA450411 to 493 MHzJCDMA832 to 925 MHzKPCS1750 to 1870 MHzGPS1574.4 to 1576.4 MHz
For each of the frequency bands listed in Table 1 (except for GPS), one frequency range is used for the forward link (i.e., downlink) from a base stations to a mobile wireless device, and another frequency range is used for the reverse link (i.e., uplink) from the mobile wireless device to the base stations. For example, for the cellular band, the 824 to 849 MHz range is used for the reverse link, and the 869 to 894 MHz range is used for the forward link.
Due to the need to support the multiple frequency bands of operation, it is necessary to separate RF energy between the bands. The separation prevents unintentional interference of signals transmitted in a first frequency band with signals being received in one or more other frequency bands. However, to stringently separate the bands, a large amount of attenuation at the unwanted frequencies is required. The consequence of this high attenuation is a higher insertion loss in the pass band, thus degrading the sensitivity of the receiver.
A GPS receiver that has to co-exist in a multi-mode phone will have inferior performance to a “stand alone” GPS receiver due to the above-described isolation requirements and the resulting insertion losses. This holds true even when there is no RF energy present at the undesired frequencies. This is particularly undesirable when the wireless device is acquiring a satellite. Typically, the tracking performance of a GPS receiver can withstand a higher noise figure when compared to acquisition; however, with the filtering components always in the signal path, all GPS signals are attenuated.
Therefore a need exists to overcome the problems with the prior art as discussed above.